The invention relates to an electron image tube comprising an image-forming screen, an electron-optical imaging system, and a trapping space for loose particles in the tube which are accommodated in an envelope.
A tube of this kind is known in the form of an X-ray image intensifier tube from GB No. 776,351. In a tube described therein, an incident image-carrying X-ray beam is converted into an image-carrying beam of photoelectrons in an entrance screen which comprises a layer of X-ray luminescent material and a photocathode. The electron-optical system converts the beam of photoelectrons into a visible image in an exit screen of the tube which also comprises a layer of luminescent material. The trapping space for loose particles is constructed as a side portion of the tube. After assembly and sealing, loose particles which are liable to remain or be formed in such a tube can be trapped in such a space. Such loose particles may consist of, for example, metal, insulating material, phosphor material or external dust, and can exert a seriously disturbing effect during operation of the tube. The particles can, for example, cause undesirable electrical charging phenomena with field emission or even electrical breakdown. Moreover, when deposited on a sensitive side of an image screen, loose particles can also directly distrub an image to be formed. However, a trapping space which projects from the tube is not very convenient.